As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent charge retention and service-life characteristics, which has been widely used as an energy source for various electronic products as well as mobile devices.
However, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or external physical impact. That is, the safety of the lithium secondary battery is very low. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as the overcharge of the lithium secondary battery or the overcurrent in the lithium secondary battery, are connected to a battery cell.
Generally, the PCM is connected to the battery cell via conductive nickel plates by welding or soldering. That is, the nickel plates are connected to electrode tabs of the PCM by welding or soldering, and then the nickel plates are connected to corresponding electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
It is necessary for the safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. Consequently, an insulation tape is generally bonded to the PCM excluding electrode terminal connection portions thereof to maintain electrical insulation, thereby achieving such connection.
In this case, however, it is difficult for the safety elements to rapidly sense the temperature of the battery cell due to the insulation tape, and, in addition, mechanical strength of the safety elements against external impact is low.
Also, if a plurality of insulative mounting members or a plurality of parts is used to solve the above-mentioned problems, a battery pack assembly process is complicated. When a large number of welding or soldering processes are carried out to configure the battery pack, the welding or soldering processes must be carried out with high precision because of the small structure of the secondary battery. As a result, a defect rate is high.
Therefore, there is a high necessity for a technology that is capable of stably coupling members mounted to the upper end of a battery cell and, at the same time, of simplifying an assembly process and rapidly sensing the temperature of the battery cell using safety elements, thereby improving safety of the battery cell.